Amino acids in which amino groups or carboxyl groups are protected with protecting groups are commonly used in production of pharmaceutical bulk drugs and intermediates such as peptides. A tri-carbobenzoxy-arginine is one of important raw material compounds in production of a peptide comprising an arginine as a component.
A method for obtaining a tri-carbobenzoxy-arginine has been reported in which a commercially available arginine is dissolved in an aqueous NaOH solution, and reacted by adding carbobenzoxy chloride and NaOH to convert the arginine into a tri-carbobenzoxy-arginine sodium salt, thereafter filtration is performed to obtain the tri-carbobenzoxy-arginine sodium salt, the tri-carbobenzoxy-arginine sodium salt is neutralized using sulfuric acid, and then extracted with ethyl acetate to synthesize a tri-carbobenzoxy-arginine (Non-Patent Document 1).
However, in the above-mentioned method, a solid is precipitated in an aggregated form in the middle stage of the reaction, so that handling is difficult for production on an industrial scale. In addition, in the above-mentioned method, a di-carbobenzoxy-arginine remains at the end of the reaction, and therefore the yield is markedly reduced. Further, in the above-mentioned method, filtration of the tri-carbobenzoxy-arginine sodium salt is performed several times, but the filtration characteristic is very poor. Thus, the method has a major problem in production on an industrial scale.